Star actors from Russell Crowe to Kirstie Alley took to Twitter to pay tribute to Horner, after trade publications The Hollywood Reporter and Variety reported he had died in his private plane.
Director Ron Howard wrote: "Brilliant Composer James Horner, friend & collaborator on 7 movies has tragically died in a plane crash. My heart aches for his loved ones."
Horner, 61, won two Academy Awards for his work on "Titanic", one for the score and one shared with lyricist Will Jennings for best original song - "My Heart Will Go On", performed by Celine Dion.
Horner also composed the music for "Aliens", "The Karate Kid", "Braveheart" and a string of other major films. His scores for "Avatar", "A Beautiful Mind" and "House of Sand and Fog" earned Oscar nominations.
His attorney Jay Cooper told Reuters he had not heard from Horner since the crash, but could not confirm whether he was on board at the time. "He`s an experienced pilot, but I know nothing else," Cooper said.
The Ventura County Fire Department said the plane crashed at 9:30 a.m. (1630 GMT Sunday) and there were no survivors. The cause of the crash was not immediately known.
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